Electric and acoustic stimulation (EAS) type cochlea implantation surgery

INTERVENTION: The EAS choclea implantation is performed under general anesthesia. Same as standard cochlea implant surgeries, an antromastoidectomy is performed, followed by an atticotomy and posterior tympanotomy and insert cochlear implant electrode to cochlea and fix implanted electrode and signal receiver from speach processor. A EAS cochlea implant electrode is inserted into the cochlea, using a round window aproach (Adunka et al.,2004; Skarzynski et al.,2007). This electrode insertion technique is able to preserve residual hearing in low frequencies. CONDITION: Bilateral profound sensorineural hearing loss PRIMARY OUTCOME: The therapeutic effects are evaluated at 6 month and 12 month after the EAS operation, using the free field audiometry and speech recognition threshold test. ; ; In the free field audiometry test, marked recovery is defined as more than 30 dBSPL recovery in the mean hearing level at the 2000Hz, 4000Hz and 8000Hz.; ; In the speech recognition threshold test, marked recovery is defined as any recovery of the maximum speech recognition score (%) by speech recognition threshold test using 67S or 57S Japanese monosirable word tabele (Japan Audiological Society 1967, 1957). SECONDARY OUTCOME: The secondary outcome are evaluated at 3 month and 6 month after the EAS operation, using pure tone audiometry. In this test, marked effective is defined as less than 40 dBSPL deterioration in the mean hearing level at the 125Hz, 250Hz and 500Hz. INCLUSION CRITERIA: Adult bilateral profound sensorineural hearing loss patient with a ski‐slope type hearing loss corresponding to the frequencies listed here: 1) 125Hz, 250Hz, and 500Hz are under 65dB. 2) 2000Hz is over 80dB. 3) 4000Hz and 8000Hz are over 85dB. One of the above mentioned frequencies may be out of the mentioned decibel lebels by 10dB still be considered as a subject. The maximum speech recognition score in quiet of EAS subject should be under 60% at 65dB in the best aided condition wearing the hearing aid.